Electrical Power

Gearbox-driven generation, DC/AC distribution, protection and the battery/essential bus.

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Main ideas

Helicopter electrical systems use the same principles as fixed-wing: an engine/gearbox-driven generator or alternator, a battery, and provision for external ground power, feeding DC and (on larger types) AC busbars.
AC where fitted may be produced by an inverter or an engine-driven AC generator; transformer-rectifier units (TRUs) supply DC from AC; busbars, bus-ties and load-shedding manage distribution.
PROTECTION is by generator control units and circuit breakers; the battery provides start power and an emergency reserve for essential loads (instruments, warnings, radios).
The generator is usually driven from the main gearbox, so it keeps running in autorotation as long as the rotor turns.
Key electrical loads include the tachometer/HUMS, warning systems, avionics and (where fitted) anti-ice and stability-augmentation systems.
⚠ Exam trap: helicopter electrical generation/distribution follows the same generator-plus-battery-plus-protected-busbars pattern as fixed-wing; the generator is typically gearbox-driven, so it continues to supply power during autorotation while the rotor turns.

Solved examples

During an autorotation after an engine failure, does the helicopter lose all electrical power?
Not necessarily. The generator is driven from the main gearbox, which is turned by the autorotating rotor, so as long as the rotor keeps turning the generator can continue to supply power. Even if generation is lost, the battery feeds the essential bus (instruments, warnings, radios) for the descent. This is why essential loads are prioritised on the battery/essential bus.

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